docs: def _get_database(self, database_name):
          """
          Get PyMongo client pointing to the current database.
  
          :return: MongoDB client of the current database.
          :raise DataSourceError
          """
          try:
              return self._client[database_name]
          except InvalidName as ex:
              raise DataSourceError("Cannot connect to database %s!"
                                    % self._database) from ex